Underwater craft for transporting divers

ABSTRACT

An underwater craft or scooter adapted to transport a diver underwater and having a hull, a screw for propulsion of the hull, an electric motor for driving the screw through a propeller shaft, a storage battery for supplying power to the motor, and a control system for controlling the supply of power. Various improvements are provided, among which is a transparent water shield for shielding the operator from the relative flow of water past the hull in motion, a trimming device for fore-and-aft balancing of the hull, a device for reducing moisture in the hull, a system for detecting and indicating water in the hull, apparatus for protecting electrical parts from moisture and battery gases, a system for discharging battery gases out of the hull, a device for preventing infiltration of battery gases to and into electrical parts, and a device for preventing leakage of battery electrolyte to parts surrounding the battery.

United Statesv Patent 1 [1 1 3,757,721 14 1 Sept. 11, 1973 UNDERWATER CRAFT FOR TRANSPORTING DIVERS Yasuhiro Ohishi, 26-34, S-chome, Nakano, Nakano-ku, Tokyo, Japan 22 Filed: Feb. 23, 1972 21 App]. No.: 228,578

[76] Inventor:

FOREIGN PATENTS OR APPLICATIONS 12/1964 Australian, 114/16 A Primary Examiner-Milton Buchler Assistant Examiner-Stuart M. Goldstein Attorney-Eric H. Waters, John G, Schwartz et a1.

57 ABSTRACT An underwater craft or scooter adapted to transport a diver underwater and having a hull, a screw for propul sion of the hull, an electric motor for driving the screw through a propeller shaft, a storage: battery for supplying power to the motor, and a control system for controlling the supply of power. Various improvements are provided, among which is a transparent water shield for shielding the operator from the relative flow of water past the hull in motion, a trimming device for fore-andaft balancing of the hull, a device for reducing moisture in the hull, a system for detecting and indicating water in the hull, apparatus for protecting electrical parts from moisture and battery gases, a system for discharging battery gases out of the hull, a device for preventing infiltration of battery gases to and into electrical parts, and a device for preventing leakage of battery electrolyte to parts surrounding the battery.

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UNDERWATER CRAFT FOR TRANSPORTING a lDlVERS BACKGROUND OF THE INVENTION This invention relates generally to submarine or underwater crafts, machines, and devices and more particularly to a new and advanced underwater craft of a type which may be called an underwater scooter," and which can be used to carry or tow one or more underwater divers.

The design of an underwater craft of this character is much more difficult than one would at first conclude and requires the solution of several difficult problems.

One. of the principal problems is the presence of water within the enclosed parts of the craft which accommodate the motive power means, the electrical system, and related parts. One source of this water is water condensed by the difference between the original temperature of the air with the enclosed parts and the temperature of the underwater environment. While the quantity of this water is not large, this water is troublesome in that it can reach all exposed interior parts of the craft. Another source of water is water which infiltrates from the underwater environment into the craft interior and accumulates therewithin as bilge water. Any water or moisture within-the craft is undesirable because it causesshort-circuiting of the electrical system and corrosion of metal parts.

i A related problem is leakage of water into the craft through parts such as the hull part where the shaft of the screw propeller extends out of the hull.

Another diffiCUIl; problem is the generation of gases from the electric storage battery. In the present state of the art, a battery of the type containing an electrolyte is the most practical source of power for propulsion, illumination, and other purposes in an underwater craft of the instant character, and the generation'of gases from thebattery. These gases must be effectively exhausted out of the craft, and the electrical system must be shielded from these gases in order to prevent ignition thereof and the consequent explosion.

Still another problem, related to the problem of battery gas generation, is the leakage of the electrolyte from the storage battery.

Still another problem is the necessity of a switching device for initially connecting several of the battery cells in series with the main motor and connecting several of the cells inparallel with the motor when the voltage decreases or when lowering the speed. Such a switching procedure is necessary for efficient utilization of the energy stored in the battery.

A further problem is the tendency of a craft of this character to lose its fore-and-aft balance when it is carrying or towing a diver. in addition, direct exposure of the diver to the flow of water relative to the moving craft gives rise tofatigue and discomfort.

Some of these problems will be described more fully hereinafter in connection with the solutions thereto afforded by this invention.

SUMMARY OF THE INVENTION there is provided an underwater craft adapted to transport one or more divers underwater and comprisinga hull, a screw for propulsion of the null, an electric motor for driving the screw through a propeller shaft, a storage battery for supplying power to the motor, a control system for controlling the supply of power, a handlebar secured to the hull for grasping by at least one diver, a transparent water shield mounted on the hull'for shielding the diver from the relative water flow past the hull in motion, a trimming device for diverting the relative water flow thereby to trim the hull in pitch to overcome unbalance due to the weight of the diver bearing on the hull, means for minimizing leakage of outside water into the hull, means for reducing condensation of moisture in the hull, means for protecting electrical parts within the hull from moisture and gases, means for detecting and indicating water in the hull, means for discharging battery gases out of the hull, means for preventing infiltration of battery gases to and into electrical parts, and means for preventing leakage of battery electrolyte out to parts surrounding the battery.

The nature, utility, and further features of this invention will be apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings, in which like parts are designated by like reference numerals.

BRIEF DESCRIPTIONOF THE DRAWINGS showing the principal internal parts and arrangement thereof within the hull of the same underwater scooter;

FIG. 4 is a relatively enlarged, fragmentary plan view showing an access device for battery charging and exhausting of battery gases;

FIG. 5 is a vertical section taken. along the plane indicated by line V-V in FIG. d as viewed in the arrow direction;

FIG. 6 is an enlarged, fragmentary view, in vertical section, showing the details of a device for discharging heat within the scooter hull to the underwater environment;

FIG. 7 is a plan view showing a transparent waterflow shiled provided around the piloting area of the sooter;

FIG. 8 is a verticalsection taken along the planes indicated by bent line Viil-Vlll in FIG. 7 as viewed in the arrow direction;

FIG. 9 is a stern elevation of the scooter, showing one example of a stern hydroplane for fore-and-aft trim ming of the underwater scooter;

FIG. 10 is a side (port) elevation, orthogonal to FIG. 9, showing the stern end of the scooter and the stern hydroplane;

FIG. 11 is a stern elevation of the scooter, showing a deflecting ring orcowling disposed around the propulsion screw of the scooter and constituting another example of a trimming device;

FlGplZ is a side (port) elevation, orthogonal to P16. ill, showing the stem end of the scooter and the deflecting ring;

I byline XVI-XVI in FIG. as viewed in the arrow direction;

FIG. 17 is a vertical, longitudinal section, partly in schematic form, showing one example of a device for detecting and indicating the presence of water which has infiltrated into the hull;

FIG. 18 is a fragmentary vertical section, partly in schematic form, showing another example of a device for detecting and indicating the presence of water in the bottom or bilge of the hull;

FIG. 19 is a side (port) elevation, which parts cut away, indicating the manner in which a cable of gastight construction is installed in conjunction with a sealed terminal box to prevent infiltration of battery gases into an electrical distribution compartment;

FIG. 20 is an enlarged cross section showing the construction of the above mentioned cable;

FIG. 21 is a vertical, longitudinal section showing the details of one example of a sealed terminal box used in conjunction with the above mentioned cable;

FIG. 22 is a vertical, longitudinal section showing the details of another example of the sealedterrninal box;

FIG. 23 is an enlarged, fragmentary view, mostly in vertical section, showing a part of another device for exhausting battery gases;

FIG. 24 is a combination of enlarged, fragmentary views, one in side elevation and the other in vertical section, showing the essential parts of the above mentioned device;

FIG. 25 is a longitudinal section showing an intermediate coupling in the gas exhaust pipe of the device shown in FIGS. 23 and 24;

FIG. 26 is a vertical section showingthe manner in which the downstream end of the gas exhaust piep is secured to the outlet at the hull;

FIG. 27 is a vertical section showing an example of a device which permits the escape of only gases out of a storage battery cell and prevents leakage out of the battery electrolyte;

FIG. 28 is a side elevation, with a part cut away, showing devices as shown in FIG. 27 surrounded by a mass of fibI'OUS' material which is enclosed within a cover structure;

FIG. 29 is an enlarged, fragmentary view, in vertical section showing one of the devices shown in FIG. 28;

FIGS. 30 and 31 are enlarged vertical sections shown other examples of devices for permitting the escope of gases without leakage of electrolyte out of a battery cell;

FIG. 32 is an elevation, with parts cut away, indicating the manner in which an additional quantity of the electrolyte can be accommodated;

FIGS. 33 and 34 are elevations, with parts cut away, showing a further example of a device for preventing leakage of electrolyte out of battery cells and the provision of through holes in the cell walls for equalization of pressures and electrolyte levels;

FIG. 35 is a circuit diagram showing the essential or ganization of a device for switching the motor power source for efficient operation and for preventing excessive discharging of the power source;

FIG. 36 and the part of FIG. 37 shown by full lines are partial circuit diagrams indicating a magnetic relay in the state for serial connection of storage batteries;

FIG. 37 in the part thereof shown by intermittent lines is a partial circuit diagram indicating the realy in the state of parallel connection of the batteries;

FIGS. 38(a) and 38(b) are respectively an axial elevation and a side elevation showing the exterior of a printed-coil motor according to this invention;

FIG. 39 is a vertical section taken along the plane indicated by .lineXXXIX XXXIX in FIG. 38(a) as viewed in the arrow direction; and

FIG. 40 is a circuit diagram showing one example of an electrical system for controlling overcurrent in the motor of the underwater scooter.

DETAILED DESCRIPTION The exterior appearance of one example of an underwater scooter embodying this invention is shown in FIGS. 1 and 2. The main body or structure of this scooter is a torpedo-like hull 1 having a bow or forward end on the left and a stem or aft end on the right as viewed in FIGS. 1 and 2.

The hull 1 is provided at its stern with vertical and horizontal tail fins 13 and 13a, a propulsion screw 16 disposed aft of the tail fins, and a screw ring or cowling 18 disposed around the screw to prevent objects, including divers, from contacting the screw. The hull 1 is provided further at its upper midship part with a handlebar 2, a water shield 10, switches 21 and 22, a socket 17 for recharging of the battery, and a meter 19 for indicating the over-discharged state of the battery.

The hull 1 contains therewithin a motor 14 for driving the screw 16 through a propeller shaft 15, a storage battery 29 (as shown in FIG. 3) for supplying power to the motor 14 and other devices, an accumulating tank 25, a sealed inflatable container 27, and a device 37 for discharging water which has infiltrated into the hull, all

described more fully hereinafter.

In accordance with this invention, in one of its aspects, there is provided a water shield 10, as mentioned briefly hereinabobe, whereby when the operator or diver grasps the handlebar 2 to operate the scooter in submerged state, he can travel underwater in comfort without being subjected to the full force of the water flow relative to the scooter.

The scooter hull 1 of torpedo-like shape is made of a hard synthetic resin or some other suitable material or materials. The handlebar 2 is U-shaped as viewed in plan, and its free ends 3, 3, which are directed forward, are secured by fastening means 5, 5 to projecting brackets 4, 4 respectively fixed to the starboard and port sides of the hull. The lower ends of starboard and port support members 6, 6 are secured to the free ends 3, 3 of the handlebar immediately aft of the projecting brackets'4, 4. The upper parts of these support members 6, 6 are bent horizontally toward the stem to form mounting parts 7, 7, which are provided therealong with a plurality of through holes 8 for adjustment.

The water shield 10, as best shown in FIGS.7 and 8, is made of a transparent material and has a roof part 10a and a bottom part 10b. The bottom part 10b is pro vided with two rows of through holes 11 adapted to align with the holes 8 in the mounting parts 7, 7. Thus the water shield 10 can be mounted in a manner permitting free forward-and-off movement and adjustment by fastening means 9 passed through the throughholes 8 and 11. 1H1-t On the upper part of the hull 1, forward of the handlebar 2, there is provided a flat part constituting a dashboard, on which are provided the receptacle or socket 17 for insertion of a pronged plug of an electric cord when the battery 29 is to be recharged, a battery gas discharge outlet (not shown) which can be covered together with the socket 17 by one cover member, the meter 19 for indicating the discharged state of the buttery, switches 21 and 22, and other devices such as an ultrasonic transceiver (not shown).

By the above described arrangement of parts and devices, the resistive force of the water during underwater operation is borne by the water shield 10 mounted with freedom to move forward-and-aft on the support members 6, 6. Accordingly, the operator or diver (not shown) holding onto the handlebar 2 is not subjected directly to this water force and is therefore able to operate the underwater scooter, particularly the various controls such as the switches 21 and 22, in an accurate and errorless manner.

Furthermore, the fore-and-aft mounting position of the water shield 10 can be adjusted to suit the operator by unfastening the mounting fasteners 9, changing the relative positions of the matching through holes 8 and 11, and refastening the mounting fasteners 9.

Thus, the operator can maintain his head within the water shield 10, whereby he can view the switches 21 and 22, the meter 19, and other instruments as well as the space forward of the scooter without discomfort or disturbance by direct contact with flotsam and sea weeds. Accordingly, the operator can operate the scooter with ease and comfort while avoiding dangers such as collision and descending to excessive depths.

When the operator grasps the handlebar 2 and assumes his riding position astern thereof, his weight bears down upon the rear end of the scooter, and the fore-and aft balance of the scooter is thereby disturbed. Consequently, the bow of the scooter rises, and the scooter tends to surface and plane along the water surface. This undesirable result is prevented in accordance with this invention by providing a trimming device at the stem end of the scooter.

In one example of this trimming device as illustrated in FIGS. 9 and 10, a trimming hydroplane 38 is hinged at its horizontal leading edge to the aft end of the screw ring 18 and is thereby pivotable about the hinge to vary its angle of attack or trim angle. This hydroplane 38 is provided at its lateral ends, at positions removed from the hinge line, with holding devices such as combinations each of a threaded pin 39 and a wing nut engaged therewith. Each pin 39, which is fixed at one end to the lateral end of the hydroplane and extends laterally outward, is slidably engaged in an arcuate guide slot 41 in a respective guide member 40 fixed to the hull l or the ring 18.

By the above described arrangement, a suitable trim angle can be selected and the hydroplane set at that angle simply by tightening the two wing nuts. The bydroplane thereupon functions as a waterfoil to lift the stern of the underwater scooter and thereby to counter the tendency of the scooter to assume a pitch orienta tion as indicated by arrow a.

In another example of the trimming device as illustrated in FIGS. 11 and 12, a downwardly deflected screw ring is used. This ring has a leading-edge part 18b, which has the shape of a right-circular cylinder for mounting the ringon the trailing edges of the tail fins l3 and 13a, and a downwardly deflected main part 180 contiguously aft of the part 18b. This ring functions similarly as the trimming hydroplane 38 of the preceding example in maintaining the fore-and-aft trim balance of the underwater scooter when it is being operated underwater by a diver.

According to this invention in another aspect thereof, there is provided a novel bearing device for the propeller shaft, which bearing device is highly efficient as a bearing and, at the same time, is highly waterproof.

In one example of this bearing device as illustrated in FIGS. 13 and 14, there is provided a bearing housing 42 formed integrally with the hull 1 of the underwarer scooter at the stern extremity thereof. This bearing housing is in the form of a hollow cylinder coaxially disposed around the propeller shaft 15 and at its inner end has an internal flange 43 extending inward toward the shaft axis but not contacting the shaft.

The bearing housing 42 accommodates therewithin, in sequence from the internal flange 43 aft toward the stern, a sealing ring 44 of X-shaped or H-shaped cross section, a spacer ring 45 of channel cross section with flanges directed inward toward the shaft axis, another sealing ring 46 similar to the ring 44, a lubricantless ring 47, and a cap covering the stem end of the bearing housing 42 and having an inner sleeve 54 interposed coaxially between the bearing housing and the lubricantless ring 47.

All of the above named parts within the bearing housing 42 are coaxially disposed around the propeller shaft 15, the rings 44 and 46 and the lubricantless ring 47 being in contact with the'shaft. An annular space is formed between defined by the shaft 15, the rings 44 and 46, and the ring 45 and contains a lubricating oil 48, which is a grease-like lubricant of the consistency of soft mud and is prevented from leaking out by the rings 44 and 46.

The inner or forward end of the propeller shaft 15 is coupled by a universal joint 51 to the motor shaft 50 of the motor 14.

As described above with respect to one example, the propeller shaft bearing device of this invention is of extremely simple construction andorganization. F urthermore, the use of the rings 44 and 46 afford positive prevention of leakage of the lubricating of the oil 48, whereby not only is the consumption of the lubricating oil 48 minimized, but the smooth rotation of the propeller shaft 15 is attained.

Furthermore, since the bearing housing 42 is formed integrally and simultaneously with the hull l, a great reduction in" the manufacturing cost is afforded, and the bearing device can be greatly simplified. Accordingly, in comparison with conventional bearing devices, which are ordinarily assembled aggregates of various parts, the bearing device of this invention has high strength and durability and is highly waterproof with respect to water under pressure.

According tothis invention in still another aspect thereof, there is provided a heat-transmitting or cooling device for preventing formation of dew drops due to condensation of moisture within the hull l of the underwater scooter. This device comprises, essentially,

one or more plates of a metal which is capable of transmitting and releasing heat rapidly from the interior of the hull 1 to the outside water. These plates are disposed in a part of the hull which is in contact with the outside water.

In one example of this dew preventing device as illustrated in FIGS. 1 and 6, a tapped hole 57 is formed in a part of the hull l which contacts the outside water, such as the hull bottom or the side wall. The threaded part of a flanged plug plate 58 is screwed into engagement with this tapped hole 57 until the flange of the plug plate 58 bears firmly on an O-ring 59 interposed as a packing between the plate flange and the hull l.

The plug plate 58 is made of a metal having a high thermal conductivity whereby heat within the hull 1 can be rapidly released to the outside water, and the interior temperature of the hull 1 is caused to approach that of the outside water. The metal plate alternatively can be made in the shape of a plate 58a without a flange or threaded part and fitted in depression formed in the inner surface of the hull 1.

In this manner, deposition of moisture droplets on parts within the hull 1 is prevented. More specifically, the hull interior temperature in summer in a temperate zone is of the order of from 50 to 60C, while the outside water temperature is of the order of from 10 to 20C. Consequently, this temperature difference causes moisture to condense and be deposited as dew droplets on parts within the hull. However, one or more of the metal plates 58 or 58a provided in accordance with this invention release the heat within the hull 1 to the outside water thereby to lower the temperature within the hull to a value of the order of from 25 to 30C and prevent the formation of moisture droplets.

Accordingly, short'circuiting of electrical components and conductors by condensed moisture and corrosion of metal parts due to this moisture are prevented, whereby the serviceable life of the entire underwater scooter is prolonged. Furthermore, impairment or damage due to high temperatures within the hull to various parts, such as softening of the inner regions of the hull is prevented by the lowering of the hull interior temperature by the above described cooling device according to the invention.

For further protection of electrical parts from condensed moistrue within the hull, this invention provides moistureproof housings for installation of electrical components.

In one example of these moistureproof housings as illustrated in FIGS. and 16, there is provided a base plate 61 made of a material such as aluminum and secured by screws 67 to and around the rim of the open end of a cylindrical housing structure 64 closed at its other end and made of a hard synthetic resin or aluminum. An O-ring 66 is interposed between the base plate 61 and the housing structure 64 to prevent infiltration of moisture. Thus, the base plate 61 and the housing structure 64 constitute a fully sealed housing.

The inner surface of the base plate 61 is lined with a layer of a moisture-absorbant material 62 such as a cotton fabric, a non-woven fabric, or a paper. The housing structure 64 is lined over its inner surface with a thermal insulation casing 65 made of a material such as a foamed styrol resin. As annular moisture-absorbing ring 63 having a semicircular cross section and made of cotton, a non-woven fibrous material, or the like is secured onto the inner surface of the layer of the moisture-absorbant material 62 by means such as an adhesive.

The moistureproof housing as described above is in its assembled state. Prior to the securing of the housing structure 64 to the base plate 61 as described above, one or more electrical components such as switches and transformers are mounted in insulated state on the inner side of the base plate 61, or a mounting plate (not shown) on which the electrical components have been previously mounted is secured to the inner side of the base plate. The housing structure 64 is then secured by screws 67 to the base plate 61 with the O-ring 66 interposed therebetween.

Thus, the electrical component or components are fully enclosed and protected from moisture droplets within the hull. Any moisture originally existing within the above described moistureproof housing and tending to condense is rapidly absorbed by the moistureabsorbant layer 62 and the moisture-absorbing ring 63. Mosture absorbed by the layer 62 and tending to migrate toward the thermal insulation casing 65 is absorbed by the ring 63 and thereby prevented from reaching the casing 65.

Thus, the electrical components thus housed and protected within the moistureproof housing according to this invention is protected from short-circuiting and corrosion due tocondensed moisture or water which has infiltrated into the hull.

This invention further provides a device which detects and indicates the presence of water which has infiltrated into a part of the interior of the hull 1 such as a compartment 68 as shown in FIG. 17. In this example, the compartment 68 is disposed between the motor 14 and the stern of the hull l and contains a universal joint 51 coupling the output shaft 50a of a speed-reduction device to the propeller shaft 15.

The example illustrated in FIG. 17 of the water detection and indication device of this invention comprises two spaced-apart switch electrode 76 and 77, which are directed downward and have tips which are at a specific height above and relatively near the bottom of the compartment 68, an insulator tube passed through a through hole 72 in a bulkhead partition of the hull 1, an electric power source 79 within the hull, an indicating lamp 78 connected at one terminal thereof to one electrode of the power source 79, and conductor wires 74 and 75 respectively connecting the switch electrode 76 to the other terminal of the lamp 78 and the switch electrode 77 to the other electrode of the power source 79.

When water 69 infiltrates into the compartment 68 and rises to a level such as to cause electrical contact between the switch electrodes 76 and 77, the electrical circuit comprising the above named parts is closed, and power issupplied by the power source 79 to light the indicating lamp 78 thereby to indicate the existence of water 69 of a predetermined quantity. For draining out this water 69, a tapped drain hole 700 is provided in the bottom of the compartment 68 and is normally closed by a screw plug 70.

In another example of the water indicating device according to this invention as illustrated in FIG. 18, two conductor plates 86 and 83 are disposed parallelly and apart, one above the other. The lower conductor plate 83 is supported directly on an electrically insulating mounting plate 82 secured to the inner surface of the bottom of the hull l. The upper conductor plate 86 is 

1. An underwater craft for transporting one or more divers underwater, comprising, in combination, a hull having upper and lower parts as well as inner and outer surfaces, a screw for propulsion of said hull, an electric motor for driving said screw through a propeller shaft, having a motor circuit, a storage battery with a plurality of cells for supplying electric power to said motor, including a power-source circuit and a system for controlling the supply of power; a handlebar secured to the exterior of said hull for grasping by at least one diver; a trimming device for diverting water flow past said hull, thereby to trim said hull in pitch to overcome unbalance due to the weight of the diver bearing on said hull; a propeller-shaft bearing for minimizing leakage of outside water into said hull; a device for reducing condensation of moisture in said hull; a device for protecting electrical parts from the moisture and from gases; a device for detecting and indicating water in said hull; a device for discharging battery gases out of said hull; devices for preventing infiltration of the battery gases to and into said electrical parts; a device for preventing leakage of battery electrolyte to parts surrounding said battery; and a device for preventing excess current or overcurrent in said motor; in which said motor is a waterproof printed-coil motor of small dimension in the axial direction; said hull is provided with vertical and tail fins and a ring or cowling disposed around said screw and fixed to said tail fins, and said trimming device includes a horizontal trimming hydroplane hinged at its leading edge to said ring to be pivotable about a horizontal hinge axis, and a mechanism for adjustably setting the angle of attack or trim relative to the screw axis.
 2. The underwater craft as defined in claim 1, in which said propeller-shaft bearing includes a cylindrical bearing housing formed integrally with said hull at the stern extremity thereof and disposed coaxially about said propeller shaft, two spaced-apart sealing rings of X-shaped cross section disposed around and in contact with said shaft and contained within said housing, a spacer ring of channel cross section with flanges directed inward toward said shaft, said spacer ring being interposed between said sealing rings and disposed coaxially around said shaft with an annular space therebetween, adapted to receive a grease-like lubricant, a lubricant-less ring disposed coaxially about said shaft aft of the aftmost one of said sealing rings, and a cap ring secured to the aft extremity of said hull and disposed around said shaft to hold said lubricant-less ring in place.
 3. The underwater craft as defined in claim 1, in which said device for reducing condensation includes, essentially, at least one plate of a metal capable of transmitting and releasing heat rapidly from the interior of said hull to the outside water, said at least one plate constituting a part of said outer surface of the hull and thereby directly contacting the outside water during operation or being disposed in contact with said inner surface of the hull at a part thereof where said outer surface of the hull is in contact with the outside water during operation.
 4. The underwater craft as defined in claim 1, in which said device for discharging battery gases includes a gas discharge manifold for collecting the gases from said battery cells, an accumulating tank adapted to contain an absorbent material and receiving the gas thus collected to remove the moisture therefrom, an elastic inflatable container for temporary retention of the gas thus rid of moisture, a gas exhaust pipe connected at one end to said container, a gas exhaust outlet provided through said upper part of the hull to the outside thereof and connected to the other end of said exhaust pipe, and a detachable, watertight cover for the outer side of said exhaust outlet, said cover being adapted to cover also and simultaneously an electrical receptacle provided on said outside of the hull for insertion thereinto of prongs of a plug of an external conductor cord for recharging said battery.
 5. The underwater craft as defined in claim 1, in which said device for discharging battery gases includes partition walls dividing the interior of said battery into said cells thereof and having through holes at the upper parts thereof to permit the battery gases to collect in said upper part of at least one cell, a discharge fitting installed in an upper wall of said one cell for conducting the battery gases out of said battery, a gas exhaust pipe connected at one end to said fitting, a gas exhaust outlet provided through said upper part of the hull to the outside thereof and connected to the other end of said gas exhaust outlet, and a detachable, watertight cover for the outer side of said exhaust outlet, said cover being adapted to cover also and simultaneously an electrical receptacle provided on said outside of the hull for insertion thereinto of prongs of a plug of an external conductor cord for recharging said battery.
 6. The underwater craft as defined in claim 5, in which said fitting includes a gas discharge plug screwed at its lower part into a tapped hole in said upper wall of the one cell and extending upward from said upper wall, said plug having a gas discharge hole formed therethrough, a swivel fitting fitted rotatably around said plug and having a passage communicating at one end with said discharge hole and extending at the other end to an opening at the outer extremity of an outlet tube for connection to said exhaust pipe, a cap nut screwed onto the upper part of said plug to hold said swivel fitting down against said upper wall of the one cell, and annular packings interposed respectively between said cap nut and said swivel fitting, as well as between the latter and said upper wall.
 7. The underwater craft as defined in claim 1, in which said battery is installed in a battery compartment separated from a power distribution compartment by at least one bulkhead, and the electric power is conducted from said battery to said distribution compartment by way of a sealed terminal box and a cable passed through said at least one bulkhead, said cable including a plurality of insulated conductor wires in substantially parallel, spaced-apart disposition, an outer cable cover encompassing said wires and spaced apart therefrom, and a filler of a material resistant to acids and alkalis, and of a consistency of soft mud, filling the spaces between said cover and said wires, and between said wires themselves.
 8. The underwater craft as defined in claim 7, in which said terminal box includes a hollow cylinder having ends closed in a gas-tight manner respectively by first and second end walls, said second end wall being secured to said at least one bulkhead, partly defining said battery compartment, a through hole being formed through said second end wall and said bulkhead for insertion therethrough and into said cylinder of one end of said cable, a plurality of terminal structures inserted through holes in said first end wall to project into the hollow interior of said cylinder and connected respectively at the parts thereof thus inserted to the ends of said conductor wires of the cable thus inserted into said cylinder, the outer parts of said terminal structures being adapted to be connected to respective lead wires to electrodes of said battery, packings interposed between said terminal structures and said first end wall to prevent infiltration of gases and moisture into the interior of said cylinder, and a packing interposed between said cable and said second end wall.
 9. The underwater craft as defined in claim 8, in which said cylinder is formed integrally with said at least one bulkhead.
 10. The underwater craft as defined in claim 1, in which said device for preventing leakage includes a screw plug fitting having threaded upper and lower parts, the latter being screwed into a tapped through hole in an upper wall of each of said battery cells, said plug fitting having an upper shank part, a through passage hole from the bottom surface of said lower part to an outlet port in a side flank of said shank part, and a flange adjacent said lower part, an elastic tube fitted firmly around said shank part over said outlet port and operative to permit only the battery gases to escape through said outlet port and to prevent leakage of the battery electrolyte out of said cells, a packing Interposed between said flange and said upper walls of said cells, and a cap nut screwed onto said upper part of the plug fitting.
 11. The underwater craft as claimed in claim 10, in which parts of said device for preventing leakage, above said cells, are surrounded by a mass of an absorbent, fibrous material enclosed within a cover structure fastened in a sealed manner to an upper peripheral part of said battery, whereby any electrolyte which has leaked out of said upper part of the battery is absorbed by said fibrous material and prevented from reaching parts surrounding said battery.
 12. The underwater craft as claimed in claim 1, in which said device for preventing leakage includes, with respect to each of said battery cells: a screw plug cylinder having threaded upper and lower plug parts, the latter being screwed into a tapped through hole in an upper wall of said cells, said plug cylinder having a supplementary reservoir chamber open at its lower part to the interior of said cells and having a substantial volume for accommodating excess electrolyte which may rise thereinto, said plug cylinder further having a vertical gas discharge tube disposed above said chamber and having a through passage hole from said chamber to an outlet port in the side of said discharge tube and an annular chamber formed between said discharge tube and a cylindrical outer wall of said plug cylinder, and separated from said reservoir chamber; a mass of an absorbent, fibrous material filling said annular chamber; an elastic tube fitted firmly around said discharge tube over said outlet port and operative to permit only the battery gases to escape and to suppress leakage of the battery electrolyte; a lid having a plurality of vent holes therethrough and secured to said upper plug part of the plug cylinder to close said annular chamber; and a packing interposed between said plug cylinder and said upper walls of the cells.
 13. The underwater craft as claimed in claim 1, in which the interior of said battery is divided into said cells by partition walls having through holes at least two levels thereof for continual equalization of pressures and electrolyte levels within said cells, and in which said device for preventing leakage includes, with respect to at least one of said cells: a gases discharge cylinder having an upper part and a lower threaded part, the latter being screwed into a tapped through hole in an upper wall of said one cell, said cylinder further having a gas discharge tube having a through passage hole from the bottom of said lower threaded part to an outlet port in the side of said discharge tube, an annular chamber formed between said discharge tube and cylindrical walls of said cylinder; an absorbent, fibrous material filling said annular chamber; a cap nut having vent holes and being screwed onto said upper part of the cylinder to cover said annular chamber; and a packing interposed between said cylinder and said upper wall of the one cell.
 14. The underwater craft as claimed in claim 1, in which said motor includes a main frame for mounting of said motor; a cover having the shape of a shallow pan and secured in a water-tight manner to said frame to form an enclosed and sealed interior; a bearing support secured to the outer central part of said cover and having a central part projecting slightly into said interior through a hole in said cover; coaxial bearings supported respectively by said frame and said support; a rotor shaft rotatably supported in said bearings and supporting coaxially a rotor disk secured perpendicularly to said shaft; an annular yoke made of iron and secured to said frame to confront a peripheral region of said disk on one side thereof; an annular permanent magnet secured to said cover to confront said peripheral region on the other side thereof; brushes contacting said disk; and elastic members urging said brushes into continual contact with said disk.
 15. The underwater craft as defined in claim 1, in which excess current in said motor is prevented by an overcurrent controller including a device for changing over the connection of said batteries in accordance with the motor current, and an over-current tripping device which cuts out said batteries when the motor current exceeds a predetermined value.
 16. The underwater craft as defined in claim 1, in which said controlling system includes a device for changing over the connection of said batteries, and a device for tripping said power-source circuit, wherein said changing-over device includes a voltage-drop detector inserted in said motor circuit, an electromagnetic relay connected to said detector, and a switching device operated by said relay to change over said connection from series to parallel when the motor current exceeds a predetermined value.
 17. The underwater craft as defined in claim 1, in which said device for detecting water includes two switch electrodes supported in spaced-apart, vertical disposition with downwardly directed tips at a predetermined height above the bottom of said hull, an electric power source with two output terminals, and an indicating lamp connected between one of said terminals and one of said electrodes, the other terminal being connected to the other electrode, electrical contact being established between said tips of the electrodes when water in said bottom of the hull rises to the predetermined height to fill the space therein, whereby said lamp is lit.
 18. The underwater craft as defined in claim 1, in which said device for detecting water includes first and second conductor plates supported horizontally in mutually parallel and spaced-apart disposition near the bottom of said hull at a specific height thereabove, said plates being electrically insulated from each other and from other parts, an electric power source with two output terminals, a buzzer, and a pilot lamp, one of said terminals being connected to said second plate, and said buzzer and said lamp being connected in series between the other terminal and said first plate, electrical contact being established between said plates when water in said bottom of the hull rises to the specific height to fill the space therein, whereby said buzzer is sounded and said lamp is lit. 